A film prepared from polyvinyl alcohol-based resins can be employed even in fields in which usual water-insoluble films are not appropriate because of its excellence in a retentive property of fragrance, a transparency, an oil resistance, an oxygen barrier property, a property for keeping warmth, and further a water-soluble property.
However, a polyvinyl alcohol alone is rigid, accordingly, it can not be molded without plasticizers. In the case when plasticizers are employed, there have been problems that generation of smoke in molding and bleeding of the plasticizers are accompanied.
In order to make a polyvinyl alcohol flexible, there are introduced proposed processes in which oxyalkylene groups are into the polyvinyl alcohol. For example, U.S. Pat. Nos. 1,971,662, 2,844,570 and 2,990,398 describe that ethyleneoxide is allowed to react by addition to a polyvinyl alcohol.
Furthermore, U.S. Pat. Nos. 4,618,648 and 4,369,281 describe of polymers in which vinyl acetate is graft polymerized in the presence of a polyalkylene glycol.
Still further, U.S. Pat. Nos. 4,618,648 and 4,675,360 copolymers composed of vinyl alcohol and a poly(alkyleneoxy)acrylate which can be molded by an injection or extrusion molding, and molded articles obtained have a water-soluble property and flexibility.
However, although the above-described polyvinyl alcohol having oxyalkylene groups has more flexibility than polyvinyl alcohol, it is not flexible at low temperatures, and further the flexibility has not been often satisfied depending upon uses even at room temperatures.
Therefore, it has been carried out that there are added both plasticizers and the above-described polyvinyl alcohol having oxyalkylene groups for the purpose of further improving a processability in molding.
For example, a polyethylene glycol or polypropylene glycol is employed in Japanese Patent Publication (Kokai) No. 203932/1991, and nylon 11, nylon 12, and a polyester elastomer are employed in Japanese Patent Kokai No. 271736/1994, as plasticizers.
However, a drawback of smoke in molding and bleeding is not solved in the former, and there is a drawback that the plasticizers are not only expensive but also transparency and rigidity in molded articles considerably lower in the latter.
In the meantime, a polyvinyl acetal-based resin in which a polyvinyl alcohol is acetalyzed has been employed as a interlayer for glasses, etc. due to a strong point of its transparency and rigidity, etc.
It is difficult to fabricate by molding the resin similarly to the polyvinyl acetal resins, and it is usually employed by mixing a large amount of ester-based plasticizers. Therefore, smoking in a molding process and bleeding out are occasionally caused in the above-described polyvinyl acetal-based resin similarly to the polyvinyl alcohol. Accordingly, there has been also expected an excellent plasticizer capable of employing also for the polyvinyl acetal-based resin.
In addition, there are expected inexpensive and novel plasticizers or softening agents having an excellent compatibility with polymers and high molecular weight which do not cause smoking in a molding process and bleeding out, in order to improve moldability and flexibility also in polymers other than the above-described polyvinyl alcohol and polyvinyl acetal resin.
Also, although water solubility of polyvinyl alcohol can be generally adjusted by controlling saponification degree, it is difficult to minutely adjust the water solubility in a range from gradually water-soluble level to water-insoluble level by only controlling the saponification. In the case when water solubility is adjusted only by controlling saponification, not only difficulty in adjusting the water solubility, but also other properties such as flexibility and adhesive properties have been often deteriorated.
On the other hand, there has been conventionally put into practice a study for improving flexibility of starting polymers by the addition polymerization of lactone monomers using polymers having hydroxyl groups in the molecule. For example, Japanese Patent Publication (Kokoku) Nos. 1607/1987 and 20252/1988 (corresponding to U.S. Pat. No. 4,522,904) disclose that an epoxy resin prepared by bisphenol A and epichlorohydrin is improved in flexibility by the addition polymerization of lactone monomers using the epoxy resin, resulting in becoming difficult to break even after cured.
Nothing has been reported until now that lactone monomers were polymerized by the addition polymerization to polyvinyl alcohol in spite of its capability of forecasting to a certain extent. Therefore, properties of a lactone-modified polyvinyl alcohol obtained have not been analyzed, and also the utilization in industries has not been studied.
Furthermore, the present inventors disclosed methods for preparing a graft polymer and a block polymer by the addition polymerization of a lactone monomer to starting resins in Japanese Patent Publication (Kokai) Nos. 52950/1991 and 134011/1991. Those are polymers in which a styrene-2-hydroxyethylmethacrylate-based copolymer is a main chain polymer and polycaprolactone units are graft chains.
Still further, the present inventors disclosed methods for preparing a linear polymer and a broom-shaped block polymer by the addition polymerization of lactone monomers to polystyrenes having 1-2 or 5-50 hydroxyl groups at terminal positions in the specifications of Japanese Patent Applications No. 164560/1994 and No. 251241/1994.
In addition to the above-described disclosures, the present inventors disclosed that polymers having hydroxyl groups in the molecular chain are employed as an initiator in the case of preparing polylactones.
For example, the present inventors disclosed an example that 2-hydroxyethyl methacrylate is employed as an initiator to prepare copolymerized or grafted polymers in Japanese Patent Unexamined Publication (Kokai) No. 192410/1995.
Also, the present inventors disclosed a case that a branched polylactone is prepared by the addition polymerization of a lactone monomer with polyfunctional initiators which have at least 3 functionalities, and a case that an oligomer having a radically polymerizable double bond together with a hydroxyl group such as 2-hydroxyethyl (meth)acrylate is employed as an initiator to prepare a copolymer with other radically polymerizable monomers and a graft-modified polymer with a variety of polymers, for example, a graft-modified polymer prepared from sugars, starch, and celluloses, etc., in the specification of Japanese Patent Application No. 47384/1995.
However, it is important to obtain polylactones having a high melt viscosity in processes relating to the cases, and actually, there are employed initiators having 3 to 4 functional groups in the molecule such as trimethylolpropane and pentaerythritol, etc., and it has not been almost studied that there were employed initiators having at least 10 functional groups in the molecule for preparing the polylactones.
Generally speaking, although plastic materials have been used in a variety of fields owing to its excellent properties, there has been a drawback that those readily accumulate static electricity because of its hydrophobic property. If an anti-electrostatic property can be given to the plastics materials, the use fields thereof can be further enlarged.
Specifically, it enables to enlarge the use fields such as a copy machine, facsimile, computer, printer, clothes made of synthetic textile, and parts requiring prevention of dust, etc.
Many attempts for giving an anti-electrostatic property to plastic materials have been tried until now. For example, there are mentioned methods that anti-static agents are coated on the surface of a thermoplastic resin or mixed therein.
There are disclosed a variety of processes in order to improve an anti-electrostatic property by giving a hydrophobic property to plastic materials. For example, although Japanese Patent Unexamined Publication (Kokai)Nos. 53465/1975, 6049/1979, and 38123/1985 describe that metal salts of sulfonic acid are used as an anti-static agent, there have been problems that the anti-electrostatic property remarkably decreases with lapse of time and that the anti-static agent is removed by washing with water, etc.
Furthermore, there is also known a process in order to keep long the anti-electrostatic property by mixing a resin having hydrophilic property and optionally the anti-static agent with thermoplastic resin.
As a most typical process, although a process in which a polyalkyleneoxide is used together with the metal salts of sulfonic acid is proposed in Japanese Patent Publication (Kokoku) No. 11944/1985, there are problems that not only mechanical properties and heat resistance in the polyalkyleneoxide itself are poor but also a variety of properties in resin compositions obtained sharply decline because of a poor compatibility with a thermoplastic resin having a hydrophobic property.
Even other polymers having a hydrophilic property, for example, such as polyvinyl alcohol and polyethylene glycol have similar problems.
As a case, there have been also tried many attempts for giving a permanently anti-electrostatic property to a styrene-based resin which is one of the thermoplastic resins. For example, Japanese Patent Unexamined Publication (Kokai) No. 36237/1980 discloses a process in which a vinyl-based monomer having alkylene oxide group is graft-copolymerized with rubber components in a styrene-acrylonitrile-butadiene resin copolymer (ABS resin). However, the resin obtained by graft-polymerization of a hydrophilic elastomer described in Japanese Patent Unexamined Publication (Kokai) No. 36237/1980 is prepared by a complicated preparation process, and mechanical properties in the resin obtained are not sufficiently satisfied.
Furthermore, Japanese Patent Unexamined Publication (Kokai) No. 269147/1990 discloses a process in which a copolymer composed of alkylene oxide and epichlorohydrine is added. Still further, it is known that a polyetheresteramide in which a polyamide and a polyether are connected through a dicarboxylic acid has an excellent rubber-like elasticity and a good anti-electrostatic property.
However, the polyetheresteramide is poor in compatibility with other thermoplastic resins, for example, a vinyl-based polymer such as a polystyrene, a styrene-acrylonitrile copolymer resin (AS resin), a polymethylmethacrylate (PMMA), a styrene-methylmethacrylate copolymer resin, styrene-butadieneacrylonitrile copolymer resin (ABS resin). Therefore, for example, Japanese Patent Unexamined Publication (Kokai) No. 246344/1986 discloses that a composition has a permanently anti-electrostatic property which is composed of (A) a polyetheresteramide, (B) a graft copolymer in which (meth)acrylic esters and/or aromatic vinyl monomers are polymerized with a rubber-like polymer, and (C) a copolymer (styrene-based polymer) in which a mixture composed of monomers such as a (meth)acrylate, an aromatic vinyl and/or vinyl cyanate monomers is copolymerized.
Still further, Japanese Patent Unexamined Publication (Kokai) No. 23435/1985 discloses that a mechanical strength in a composition is improved by blending a polyetheresteramide with a modified vinyl-based polymer having carboxylic groups.
Besides, Japanese Patent Unexamined Publication (Kokai) No. 163251/1989 discloses that a modified vinyl-based polymer having amino groups or substituted amino groups is employed in order to improve its mechanical strength by improving compatibility between a styrene-based resin and a polyetheresteramide and, further, Japanese Patent Unexamined Publication (Kokai) No. 70739/1990 discloses that a rubber-modified styrene-based thermoplastic resin, etc. having a vinyl monomer containing hydroxyl groups which is a component in copolymerization is employed as a third component.
Also, although the processes described in Japanese Patent Unexamined Publication (Kokai) No. 269147/1990 can improve mechanical properties, and improve permanently anti-electrostatic properties and a layer-state cleavage, the epichlorohydrin copolymer which is a primary component is expensive, resulting in that a final composition is not always low in price.
The processes described in Japanese Patent Unexamined Publication (Kokai) No. 23435/1985 also have a drawback that badness in outer appearance is caused such as silver streaks and frosting. Even in the case of thermoplastic resins for molding other than styrene-based resins, there has been desired a composition having excellent properties such as mechanical strength and thermal resistance, etc., and further permanently anti-electrostatic properties.
As a result of an intensive study for the purpose of solving the above-mentioned problems, the inventors of this invention have found that it is possible to prepare a resin having permanently anti-electrostatic properties and an excellent mechanical strength by mixing resins for molding with a suitable amount of a lactone-modified polyvinyl alcohol which has an excellent compatibility with thermoplastic resins.
Furthermore, the inventors of this invention, as a result of a further continued study for the purpose of providing a polylactone having new functions and uses by polymerizing lactone monomers, have found that a lactone-modified resin having hydroxyl groups which has a specified range in the mole number of hydroxyl groups per 1 g of a polymer and a specified range in number average molecular weight can be obtained by using a small amount of a specified starting polymer having at least 10 hydroxyl groups as an initiator.
As the polymer having many hydroxyl groups in the molecule is flexible, it can be used in a wide use such as pressure-sensitive adhesives, adhesives, materials for cured articles, molded articles such as cured sheets and cured films, plasticizers for polymers, coatings, biodegradable uses, and uses for medical treatments, etc.
In view of the circumstances as described hereinabove, as a result of an intensive study, the inventors of this invention have found that it is possible to solve the above-described various problems by a novel lactone-modified polyvinyl alcohol.